1. Field of the Invention
This invention relates to solar energy collectors and in particular to systems for heating enclosed space volumes such as greenhouses and residences.
2. Description of the Prior Art
One of the most widely used prior art devices for heating a space volume is a greenhouse. However, conventional greenhouses have several drawbacks. The transparent walls are poor insulators. Whenever the influx of solar radiation stops, heat losses are dramatic. For this reason, in northern climes, heat must be supplied by auxiliary means.
During winter months, light available for photosynthesis is limited in conventional greenhouse structures. Because the sun is at a low angle to the horizon, the amount of solar radiation falling on a given area of the horizontal plant bed is small. As a result, plants in a conventional greenhouse require excessive time to reach maturity.
Many recent examples of solar collectors used for heating enclosed space volumes incorporate an intermediate member to absorb the heat. The heat is then transferred to the space volume to be heated.
Because of the interjection of the intermediate member, none of the solar radiation reaches the ultimate energy user as visible light. Only heat is transferred.
A significant development in the area of solar energy collectors is the incorporation of external reflector/insulator panels. The panels are movable. During times of solar energy influx, a reflective surface of the panel reflects sunlight into the collector. During absence of solar energy influx, the panels are moved to a position in which they enclose the solar energy collector and insulate against heat loss. For example, see Keyes et al U.S. Pat. Nos. 3,987,786 and 3,894,685; Taylor U.S. Pat. No. 4,016,861; Arant U.S. Pat. No. 4,043,316; Atkinson U.S. Pat. No. 4,059,226; Stelzer U.S. Pat. No. 4,026,269 and Falbel U.S. Pat. No. 3,841,302.
All of these cited devices incorporate panels which extend outside of the enclosed space volume. As a result, the panels are vulnerable to the elements. They cannot be used during even slightly inclement weather because rain or snow degrade their reflectivity. Atmospheric pollutants such as dust and suspended oil alight on the reflective surfaces and diminish their reflectivity. Since the panels must enclose the solar energy collector during stormy weather, rain cannot wash away these deposits, and they accumulate and become difficult to remove.
Los Alamos Solar Laboratory has constructed an experimental Passive Solar Heated Mobil/Modular Home II. This solar heated home incorporates a movable panel which alternately reflects solar energy into the home or insulates against heat loss. However, the solar energy is absorbed in water bags from which heat is withdrawn into the living area. No visible light enters the living space through the collector. The intermediate member also adds to the complexity and cost of construction.